A group of collaborating investigators propose to characterize the control and integration of certain digestive-absorptive functions in healthy man in order to define abnormalities responsible for etiology or symptomatology in disease. Interrelated objectives comprise characterization and simultaneous quantification of major human gastrointestinal functions (secretion, transit, digestion and absorption), together with measurements of their control and coordination during a physiologic 24-hour sequence comprising three meals followed by 12 hours rest. Previously, the interactions between substances present in the small intestine during digestion which influence secretion or absorption will have been defined by more specific techniques. Secretory functions will be delineated in terms of hormonal regulation, whereas abnormalities of absorption will be examined particularly for their potential to cause diarrhea or steatorrhea. In all aspects of the proposal, particular attention will be accorded the physiologic functions and pathophysiologic significance of bile acids and their bacterial transformations. To facilitate the research, innovative tests are described; these also will have diagnostic applications in disease.